The following Nonpatent Literature 1 proposes a system that employs an LDPC code for each level of multilevel coding, as an encoding system in a multi-value modulation system. In this case, as a method of optimizing an LDPC code for each level, a probability density function that becomes an initial value at each position of a bit mapped in a modulation symbol. By using this probability density function, an optimum order ensemble (that shows a structure of a parity check matrix, and a numeral of “1” in a row or a column of the parity check matrix is expressed as an order (weight)) of the LDPC code at each bit position is obtained based on “Density Evolution”.
Nonpatent Literature 1: J. Hou, Paul H. Siegel, Laurence B. Milstein, and Henry D. Pfister, “Multilevel Coding with Low-Density Parity-Check Component Codes, 2” Proceedings of IEEE Global Telecommunications Conference, San Antonio, Tex., USA, Nov. 25-29, 2001